1. Field of the Disclosure
The field of the disclosure is that of data transmission between two apparatuses. More specifically, an embodiment of the invention pertains to a technique for transmitting one or more contents (for example video type contents), by means of a source node, on several transmission paths, to a destination node.
The invention has many applications, such as for example the transmission of video at high bit rates to a screen of a very high definition home cinema type system or else to screen panels of a showroom type system.
2. Technological Background
It is sought more particularly here below in this document to describe problems existing in the field of the transportation of high bit rate video contents through wireless systems. The invention of course is not limited to this particular field of application but is of interest for any technique for transmitting video streams or transmitting images that has to cope with closely related or similar issues and problems.
The video contents considered are for example of a resolution higher than the 1080 p standard HD format. In this case, since the bit rate needed for transmitting this type of video is greater than the bit rate currently available in 60 GHz wireless networks, the video is at least weakly compressed (for example according to what is called the chromatic sub-sampling technique).
A pixel of a video screen according to the “YUV” or “YCbCr” standard format is represented by three digital values. One is a luminance component containing information on luminosity while the other two are chrominance components containing color information. It is common for these three values to be each encoded on eight bits. The chromatic sub-sampling technique is based on the accepted principle that the human eye is most sensitive to variations in luminosity than to color variations. Based on this, the chromatic sub-sampling technique consists in eliminating a part of the chrominance information elements and regenerating them approximately according to extrapolation techniques.
60 GHz wireless systems are used to attain very high bit rates (currently of the order of 3 Gbits/s) over short ranges (of the order of about 10 meters currently). They use two prior-art antenna management techniques:                beamsteering technique by beamforming which is well suited to a point-to-point communications mode. It is used to concentrate the emission energy more efficiently on one or more desired direction. It calls for a preliminary configuring phase during which the antenna angles are adjusted so as to obtain the highest efficiency. This technique however is very sensitive to shadowing;        a wide-angle or omnidirectional antenna technique which is well suited to a mode of communications by broadcasting. This technique is less sensitive to masking than the directional technique. However, since the energy is more diffuse than in the case of the directional technique, the reception quality is thereby diminished.        
The wireless systems referred to here above have a major drawback which is their high sensitivity to shadowing. For example, the simple passage of a person on a path set up between the sender and receiver antennas cuts off data transmission between the two corresponding nodes, namely the sender and receiver nodes.
A first known solution to this problem of sensitivity to shadowing is that of installing the antennas of the system beyond the range of moving obstacles in a room. For example, the antennas are fixed at a height so that persons can freely move about in the room.
However, this first prior-art solution has the problem of requiring that audio/video apparatuses having radio interfaces be fixed at a height. This reduces accessibility to apparatuses as well as the anticipated advantage of a wireless system that would permit greater flexibility in the positioning of the apparatuses.
A second known solution to this problem of sensitivity to shadowing consists in transmitting a same piece of data several times through different paths. This technique, known as a mesh technique, relies on spatial diversity. The sender node sends data in omnidirectional mode and then a certain number of receiver nodes relay these pieces of data, thus creating a multitude of copies of the same piece of data, these copies being thus available from different geographical points of the network.
This second prior-art solution is well suited solely to the transportation of data at low bit rates such as the transportation of audio streams, but it is not suited not to the transportation of video data streams necessitating high bit rate. Indeed, the multiplication of re-transmissions consumes bandwidth. In the prior art, it is not possible to greatly increase transmissions of video data unless the video stream is very highly compressed. Now a highly compressed video stream is considered to be of mediocre or even poor quality.
A third known technique is described in the US patent document 2009/0021646. This is a method of video transmission for a wireless transmission system in which it is proposed to sub-divide the video signal to be transmitted according to groups of dots spatially grouped together and to send these groups on one or more radio channels (i.e. different paths) as a function of the conditions of transmission on the channels. In this prior-art technique:                it is sought, as a priority, to transmit the totality of the video along a determined path (main path). If possible, the other paths are used to provide information on redundancy, if the transmission errors occur on the main path;        if the main path does not enable transmission of all the video data, then the different paths are used to transmit the totality of the video data, whether distributedly or not.        
One drawback of this known third technique is that, for each transmitted packet, it necessitates also the transmission of information describing the transmitted packet (type of packet and quantity of data contained in the packet) to enable the image to be reconstituted). These information items therefore consume a part of the bandwidth (with an increase in the overhead).
One drawback of this known third technique is that, for each transmitted packet, it necessitates also the transmission of information describing the transmitted packet (type of packet and quantity of data contained in the packet) to enable the image to be reconstituted). These information items therefore consume a part of the bandwidth (with an increase in the overhead).
Furthermore, the US patent document 2009/0021646 proposes no solution whatsoever for the transmission of at least two contents (i.e. in the context of an embodiment of the present invention).
Another drawback of this third prior-art technique is that it is not suited to the transmission of compressed videos or weakly compressed videos. Indeed, the compression technique can change the quantity of information needed to represent a pixel. Typically, the techniques of compression by chromatic sub-sampling deliver a non-homogeneous stream of pixels (certain pixels being encoded with fewer bits than others). Now this third prior-art technique is not suited to managing a variable quantity of data for a pixel.